Coolant mixing in the plenum of the HPLWR three pass core

A supercritical water cooled reactor concept with multiple heat-up steps requires efficient mixing of the coolant between these steps to minimize hot spots in the core. The present study outlines the challenge of mixing in an upper mixing chamber above the core, situated between evaporator and superheater assemblies. Different measures to enhance mixing have been studied with CFD analyses, using markers at each evaporator outlet and tracing them to the superheater inlet. Even though results cannot yet be considered to be final, they indicate already the direction for further design optimization of such a high performance light water reactor. (authors)